What makes it so plausible to assume that hypocrisy is the vice of vices is that integrity can indeed exist under the cover of all other vices except this one. Only crime and the criminal, it is true, confront us with the perplexity of radical evil; but only the hypocrite is really rotten to the core.

Hannah Arendt:

Sincerity is the luxury allowed, like diadems and authority, only to the highest rank. Every man alone is sincere. At the entrance of a second person, hypocrisy begins

For every man's nature is concealed with many folds of disguise, and covered as it were with various veils. His brows, his eyes, and very often his countenance, are deceitful, and his speech is most commonly a lie.